Joost van der Westhuizen has flown to the United States to undergo clinical studies in connection with his diagnosis of a form of motor neurone disease.

Van der Westhuizen was diagnosed with amyotrophic lateral sclerosis (ALS), an aggressive form of the disease, in 2011, and he will participate in clinical studies at Massachusetts General Hospital in Boston, where the chief of neurology, Dr Merit Cudowicz, is researching the disease.

"They said I would be in a wheelchair after a year," Van der Westhuizen said in a statement. "They said I had a 20% chance to live two years. And I decided 'stuff them'. I will decide when I go."

The Rugby World Cup-winning former Springboks scrum-half will also visit the Eleanor and Lou Gehrig Centre in New York, which provides research and clinical support for sufferers of motor neurone disease and amyotrophic lateral sclerosis.

Van der Westhuizen, who has established the J9 Foundation for sufferers of the disease, hopes to establish a similar institute in South Africa. "In the beginning you go through all the emotions and you ask, 'Why me?'," he said in a statement. "It's quite simple. Why not me? If I have to go through this to help future generations, why not me?"